Step 1: Select to start a mash
While you're viewing your calendar tap on the film strip icon on the top right. This will open your mashing options. You can do this in a Classic timeline or a Freestyle timeline.
Step 2: Select the Mash option
There are three ways to mash a video. Month, Year, and Custom. Select your preferred option and the process will start automatically.
Step 3: Wait
You will be able to view the progress of your mashed video in your phone's notification window. Once done, it will offer a link to view your video within 1SE. From there you can also share your video out using the default share window provided by Android.
TIP: You do NOT have to wait until the year is over to mash your video!